Building integrated photovoltaic (BIPV) roof tiles currently represent a small portion of the overall photovoltaic market, in spite of the seemingly compelling proposition of integrating an energy source into a roofing component. Market adoption has been slow due in part to the relatively high cost of roofing tiles integrated with PV modules. High cost is currently incurred since solar modules are not designed to serve as a bulk construction material, but rather integrated into a home as a custom electrical installation. There are several barriers within the current residential rooftop BIPV market that have kept the overall market small and limited product adoption.
One of these barriers comprises of costly manufacturing processes whereby relatively expensive silicon wafers are interconnected with the often mismatched framework of a roofing tile. The solar cells are inherently costly, and their interconnection process takes time and incurs additional cost, increasing the total system cost.
Conventional BIPV roofing tile product has substantial dead space where the wafers do not fully occupy the area within the tile frame (the “open area”). This spatial inefficiency reduces the power density of the roofing tile, and requires additional tiles to be installed to achieve a particular power output for a given solar system.
Additionally, time-consuming installation processes for BIPV products such as roofing tiles, including extensive electrical wiring and mechanical interconnection between tiles, results in high system installation costs and makes operations and maintenance of installed systems cost prohibitive.
Solar modules are currently larger than typical roof tiles. The inconsistency in size and shape creates substantial integration issues.
Installation of shingles and tiles is currently performed by roofers. Installation of solar panels with these shingles and tiles, however, requires the additional involvement of an electrician on the roof, further increasing system installation cost.
While roofing has as one of its purposes the provision of thermal insulation, solar cells desire proper ventilation to keep them cool for better electrical efficiency, contradicting the thermal insulation requirement of the tile. At higher temperatures, roofing tiles incorporating PV modules perform less effectively, reducing their levelized cost of energy (LCOE).
Lack of tenability of current levels for a given module area is also an issue. Conventional silicon wafers are formed with standardized sizes, and cannot be cut to a particular size after formation. As cell photocurrent is proportional to cell area, it is not possible to tune photocurrent when the cell area is fixed.
Conventional silicon-based PV modules integrated with roofing tiles suffer from materials incompatibilities that degrade their product performance; mismatches in coefficients of thermal expansion (CTE) create stresses and strains that damage module integrity over time and with environmental exposure. Further, for those BIPV roofing tile products that incorporate plastic frameworks, the use of plastic materials exposes these modules to substantial attach upon UV exposure, and most organic materials degrade with extended sun exposure.
Drawbacks associated with traditional photovoltaic solar tiles have limited the ability and financial rationale to install large numbers of BIPV roofing in a cost-effective manner. These traditional solar tile configurations are also constrained by conventional design methodology that limit the modules to certain materials and inherit a large number of legacy parts. This combination of high material cost and conventional design hamper the ability of installers to rapidly and cost-efficiently deploy solar roofing at a large scale.
Although subsidies and incentives have created some large solar-based electric power installations, the potential for greater numbers of these large solar-based electric power installations has not been fully realized. There remains substantial improvement that can be made in BIPV roofing that can greatly reduce their cost of manufacturing, increase their ease of installation, and create much greater market penetration and commercial adoption of such products, particularly for residential installations.